1. Field of the Invention
The present invention relates to apparatus for the heat treatment of turbine blades either before, during or after work to be carried out on the turbine blades, which work involves the input of considerable thermal energy such as may occur during a welding or brazing operation.
When work is carried out to a turbine blade, which work may comprise modification or repair for example, such work involves the application of considerable thermal energy.
Applicant has found that it is advantageous to not only provide a stress relieving heat treatment after such work has been carried out but the application of controlled heat, both before the application of considerable thermal energy and in some cases during the application of considerable thermal energy, can be beneficial to reduce stresses and/or distortion that might otherwise occur to the turbine blade.
Heat may in many instances best be applied by the application of electrically heated elements, often referred to as heating mats, since the heat dissipation of such mats and the temperature to which the turbine blade is heated may be carefully controlled by altering the power supply to individual heating mats.
2. Prior Art
Problems have occurred in the past in the securing of such mats to the turbine blades and British Patent Specification No. 2,144,361, which corresponds to U.S. Pat. No. 4,613,744, provides one solution to the problem.
The invention disclosed in British Patent Specification No. 2,144,361 involved the attachment of wires to a turbine blade, which wires may subsequently be removed, to hold the heating mats in position and also enabled a part of the heating mat to be temporarily removed from a repair area to enable a work step involving welding, for example, to be carried out as required.
The attachment of heating mats in a manner as described in British Patent Specification 2,144,361 was highly satisfactory. However, in some cases problems could occur, in particular where it was required to carry out work on the turbine blade while still in position on a rotor in view of the proximity of adjacent blades, since access to the blade to be repaired can be very limited.
It is an object of the present invention to provide heating apparatus that overcomes or reduces the problems mentioned above.